Robust and orange-yellow-emitting Sr-rich polytypoid α-SiAlON (Sr 3 Si 24 Al 6 N 40 :Eu 2+ ) phosphor for white LEDs.

Nitrides and oxynitrides isostructural to α-Si ₃ N ₄ ( M -α-SiAlON, M  = Sr, Ca, Li) possess superb thermally stable photoluminescence (PL) properties, making them reliable phosphors for high-power solid-state lighting. However, the synthesis of phase-pure Sr-α-SiAlON still remains a great challenge and has only been reported for Sr below 1.35 at.% as the large size of Sr ²⁺ ions tends to destabilize the α-SiAlON structure. Here, we succeeded to synthesize the single-phase powders of a unique 'Sr-rich' polytypoid α-SiAlON (Sr ₃ Si ₂₄ Al ₆ N ₄₀ :Eu ²⁺ ) phosphor with three distinctive Sr/Eu luminescence sites using a solid-state remixing-reannealing process. The Sr content of this polytypoid structure exceeds those of a few previously reported structures by over 200%. The phase purity, composition, structure, and PL properties of this phosphor were investigated. A single phase can be obtained by firing the stoichiometric mixtures of all-nitride precursors at 2050°C under a 0.92 MPa N ₂ atmosphere. The Sr ₃ Si ₂₄ Al ₆ N ₄₀ :Eu ²⁺ shows an intense orange-yellow emission, with the emission maximum of 590 nm and internal/external quantum efficiency of 66%/52% under 400 nm excitation. It also has a quite small thermal quenching, maintaining 93% emission intensity at 150°C. In comparison to Ca-α-SiAlON:Eu ²⁺ , this Sr counterpart shows superior quantum efficiency and thermal stability, enabling it to be an interesting orange-yellow down-conversion luminescent material for white LEDs. The experimental confirmation of the existence of such 'Sr-rich' SiAlON systems, in a single-phase powder form, paves the way for the design and synthesis of novel 'Sr-rich' SiAlON-based phosphor powders with unparalleled properties.
Competing Interests: No potential conflict of interest was reported by the author(s).
(© 2024 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.)